In downlink transmission of a Long Term Evolution (Long Term Evolution, LTE for short) Rel-8/9/10 communications system, a base station, for example an eNB (evolved Node Base, evolved Node Base), sends a PDSCH (Physical Downlink Shared Channel, physical downlink shared channel) and a corresponding PDCCH (Physical Downlink Control Channel, physical downlink control channel) to each scheduled user equipment according to a scheduling result.
The PDSCH bears data sent by the eNB to the scheduled user equipment, and the PDCCH bears scheduling information of the corresponding PDSCH. The scheduling information is mainly used for indicating transmission format information to the corresponding PDSCH. The PDCCH and the PDSCH are time-division multiplexed in one subframe. The PDCCH is transmitted in the first several OFDM (Orthogonal Frequency Division Multiplexing, orthogonal frequency division multiplexing) symbols of the subframe, and the rest of OFDM symbols are used for transmitting the PDSCH. In a subframe, the PDCCHs of all scheduled user equipments are multiplexed together and then sent in a PDCCH area, and their PDSCHs are sent in a PDSCH area. Each PDCCH is comprised of 1/2/4/8 control channel elements (Control Channel Element, CCE), and the number of CCEs constituting each PDCCH is dependent on the size of the PDCCH and the channel of a user equipment corresponding to the PDCCH. The number of CCEs constituting the PDCCH may vary with different user equipments.
In a further evolution of the LTE Rel-10 system, MU-MIMO (Multiple User Multiple Input Multiple Output) and coordination among multiple cells need to be supported in order to improve the system performance, but these technologies lead to an increase in the number of user equipments that are scheduled at the same time. However, the limited capacity of the PDCCH limits the number of user equipments that can be scheduled in one subframe. Therefore, in the prior art, the PDCCH is enhanced; that is, a part of resources are divided from the original PDSCH area to transmit an enhanced PDCCH, that is, E-PDCCH (Enhanced Physical Downlink Control Channel). In this way, the capacity of the PDCCH and the number of user equipments that are scheduled at the same time can be increased. The E-PDCCH is comprised of E-CCEs (Enhance-Control Channel Element).
However, for LTE frequency-domain resources, resource scheduling is performed for the E-PDCCH in unit of RB pair (Resource Block pair). Each RB pair occupies 12 subcarriers in the frequency domain and occupies one subframe in the time domain. Resources available to the E-PDCCH are REs (Resource Element) in each RB pair except for those occupied by the PDCCH area and various reference signals. Therefore, the number of REs occupied by the E-PDCCH is significantly influenced by factors such as the system performance and actual transmission conditions, and it is difficult to ensure the number of REs occupied by each E-CCE constituting the E-PDCCH, resulting in unstable performance of E-CCEs and affecting the accuracy of reception by the user equipment.